The present invention relates to video image resizing architectures, and more particularly to a device and method for scaling a still or moving video image comprised of a first plurality of digital picture elements (known as pixels) in order to replicate the image with a second plurality of pixels.
A digital video image comprises an array of pixels, with the number of pixels in each horizontal row and vertical column being determined by the system in which the image is formed. When the image is to be displayed in a system that uses the same number of pixels in each row as the input image and the same number of pixels in each column as the input image, the image may be displayed directly. However, when the image is to be displayed in a system that uses a different number of pixels in each row and/or a different number of columns as the input image, the image must be scaled so that the same image can be displayed in the new array of pixels. For example, an image comprising a 500 by 750 array of pixels must be scaled up before it can be displayed in a system that uses an array of 750 by 900 pixels. Conversely, the same image may need to be scaled down before it can be displayed in a system using an array of only 250 by 350 pixels. As is apparent, the horizontal and vertical scaling factors may not be the same. Similar scaling steps may be required when a portion of an image on a display is to be enlarged to fill the entire display or when an image on a display is to be reduced and provided as a small inset in the display.
Digitized color video images are typically comprised of pixels that include data bits for luminance (Y) and for chrominance (U, V), and may have, for example, eight data bits for each of the Y, U, and V components (other color component systems, such as Red, Green, Blue (RGB), being equivalent.) When a color image is scaled for display in another system, each of the color components must be scaled.
Video images are desirably scaled in real-time (i.e at the rate they are delivered to the video processing system) when upscaling (increasing the number of pixels per image) or downscaling (decreasing the number of pixels per image.)
When an image is to be scaled, an input stream of pixels may be mapped to an output stream by interpolation. For example, when an image is to be scaled using linear interpolation, the input stream of pixels may be mapped into increments dx, where dx=1/K and K is a scaling factor. As illustrated in FIG. 1, with an upscaling K=3/2 (dx=2/3), an input stream of six pixels may be mapped into nine increments that will become nine output pixels. The value of each of the nine output pixels may be determined by interpolating between corresponding pixels in the input stream.
Various devices and methods for scaling video images are available. However, most do not afford real-time scaling and cannot selectively upscale and downscale with different scaling factors. Further, those devices and methods that may be able to upscale and downscale in real-time either rely on massive image pixel buffers and use complex calculations--with an associated complex array of components, or do not provide reasonable quality. For example, the scaled image may flicker, or may be incomplete because pixels, rows or columns have been skipped, or because aliasing has been encountered. Aliasing is distortion of an image caused by introduction of undesirable components into the processed signal during the scaling process and may be encountered when a signal's contents are subsampled to the point where the Nyquist sampling criterion is no longer met. Such problems typically have been handled with complex pre- or postfiltering techniques.
Accordingly, it is an object of the present invention to provide a novel device and method for scaling a video image that obviates the problems of the prior art.
It is another object of the present invention to provide a novel device and method for real-time upscaling or downscaling a video image in which interpolation and subsequent decimation are performed without skipping pixels, rows or lines to provide a high quality scaled image.
It is yet another object of the present invention to provide a novel device and method for real-time upscaling or downscaling a video image in which buffer size requirements are reduced and the number of buffers is minimized without limiting downscaling capability.
It is still another object of the present invention to provide a novel device and method for scaling a video image in which duplicate sets of interpolators and FIR filters are paired in series to provide independent vertical and horizontal scaling. to assure, and in which only two pixel or line buffers are required for downscaling.
It is a further object of the present invention to provide a novel device and method for scaling a video image in which upscaling is accomplished with a single pixel or line buffer component and linear interpolator, and downscaling is accomplished with a upscaling linear interpolator and decimating FIR filter where the number of filter taps (i.e. bandwidth) is related to the decimating factor.
It is yet a further object of the present invention to provide a novel device and method for scaling a video image in which only two line (for vertical scaling) or pixel (for horizontal scaling) buffers are required regardless of the downscaling factor.
It is still a further object of the present invention to provide a novel device and method for real-time upscaling and downscaling a video image in which the scaling factor is a combination of a predetermined upscaling factor applied in a linear interpolator and a predetermined downscaling power-of-two (i.e. binary) factor applied in a decimating finite impulse response (FIR) filter.
It is also another object of the present invention to provide a novel device and method for real-time scaling a video image in which the image is first upscaled by a scaling factor selected so that the image can be subsequently downscaled by a decimating-by-power-of-two filter to provide the desired scaled image.
It is also a further object of the present invention to provide a novel device and method for scaling a video image with full filtering to provide a bandwidth that is narrow enough to avoid aliasing.
These and many other objects and advantages of the present invention will be readily apparent to one skilled in the art to which the invention pertains from a perusal of the claims, the appended drawings, and the following detailed description of preferred embodiments.